rapid identification of group a streptococci by pyrrolidonyl-β-aphthylamide hydrolysis

in a clinical trial a new pyrrolidonyl-β-naphthylamide (pyr) hydrolysis test was compared with the bacitracin disk susceptibility test for accuracy in the presumptive identification of group a streptococci (gas). among 128 isolates of beta-hemolytic streptococci 93 group a isolates were found. the sensitivity of the pyr and bacitracin tests were similar (98.9%), but the bacitracin test had a lower specificity (80%) than the pyr test (100%). the efficiency of the pyr and bacitracin test were 99.2% and 93.7%, respectively. all bacitracin tests were performed on subcultures of the isolates from the primary plate, whereas pyr testing was performed on colonies from the primary plate. this shortened the turnaround time for the pyr test compared to the bacitracin test by at least 24 hours.